4. Self-referential ON UPDATE CASCADE and ON UPDATE SET NULL are not supported; recursion on them acts like RESTRICT. CASCADE may be nested only to 15 levels.

5. UNIQUE and FOREIGN KEY constraints checks are row-by-row, and cannot be deferred until statement end, so a row that refers to itself via a foreign key cannot be deleted.

6. A foreign key action updating or deleting a referencing table does not fire Triggers on the affected table (http://bugs.mysql.com/bug.php?id=11472). Also CASCADE foreign key updates do not update DATETIME and TIMESTAMP columns with ON UPDATE clauses.

7. After a server restart, the INNODB auto_increment counter resets to the next available value, so higher deleted key values will be re-used.

8. An accurate SELECT COUNT(*) result depends on isolation level, pending transactions, and what's in buffers and logs. If innodb_stats_on_metadata is set, INNODB updates statistics when SHOW TABLE STATUS or SHOW INDEX runs.